According to the instructions after page 1 of Form PA-8453 at 2020 Personal Income Tax Forms,
If a taxpayer elects not to use the federal self-select PIN or a return is filed without a federal return, electronic return originators (EROs) and transmitters must retain completed Forms PA-8453 and supporting documents for three years after the due date of the return or the date the return was filed electronically, whichever is later.
Any taxpayer filing electronically from a home computer must keep the signed Form PA-8453 and supporting documents for three years after the due date of the return or the date the return was filed electronically, which-ever is later.
[Bolding mine.]
